Generally, semiconductive devices are made from semiconductive wafers alternatively doped in the N and P type. Those wafers are then separated into chips. Grooves are formed at the limits of the elementary chips to be cut. The grooves are then filled with a passivating agent, for example glass; this operation is called glassivation. Then, the glass layer is scribed at its upper surface and the wafers are broken into the elementary chips. The glassivation is useful in particular for passivating the junctions emerging at the limits of the chips in case of mesa type structures (one usually differentiates the mesa type semiconductors wherein the layer limits emerge on the sides of the semiconductor device from the planar type semiconductors wherein the layer limits emerge at the level of a main surface of the chip).
FIG. 1 shows in a schematical and exemplary way an upper portion of a semiconductive device 1 comprising in particular a junction between layers 2 and 3. A groove 4 is formed and filled with a passivating glass. Thus, the glass serves to passivate the junction between the layers 2 and 3. During the last making steps of the semiconductive device, a metallization 5 is deposited onto the upper surface at the neighbourhood of the edge of the semiconductor device, close to the groove 4. Practically, it appears that the tightness between the glassivation in the groove 4 and the limit of the layer 3 is generally not sufficient and the metallization penetrates along the limit of the layer 3 and the groove 4. Such a penetration affects the performance of the semiconductive devices and can short the layers 2 and 3. Thus, the simple structure of FIG. 1 is in fact not often used in practice. For palliating the above drawbacks, one has provided in the art, above the glassivated grooves 4, an additional glassivation layer 6 as shown in FIG. 2. This glassivation layer 6 covers the groove 4 and is broader than the limits of the groove. For example, the layer 3 can have a depth in th range of 70 microns; the groove 4 a depth in the range of 100 microns and a width in the range of 300 microns; the layer 6 will have then an extension of about 200 microns away from the groove 4. Thus, even if the metallization 5 penetrates partially under the limit between the glassivation layer 6 and the above layer 3, it will not affect the performances of the device.
However, this prior art method presents in particular the following drawbacks. Firstly, the deposition of an additional localized glass layer is difficult to implement in practice when this deposition is not made inside the groove. Indeed, on the one hand it is difficult to achieve a mask for a glassivation, and, on the other hand, when one wants to deposit firstly a continuous glass layer which has then to be partially etched away, the operation is also difficult.
Another drawback of the device of FIG. 2 is that the layer 6 has in practice a thickness in the range of 10 microns while a metallization such as the metallization 5 has a thickness in the range of 1 micron. Thus, when one wishes in a further step to establish a contact between the layer 5 and an electrode, for example a pressure contact, this contact is not satisfactory because the electrode lies onto the raised glass portion 6 and not onto the metallic layer 5. In the same way, if one wishes to achieve a welded mounting, some methods cannot be used.